Printed wiring boards are manufactured by subtractive and by additive processes. In subtractive processes, the conductive pattern is obtained by selective removal of unwanted portions of a conductive foil. In fully-additive processes, the entire thickness of electrically isolated conductors is built up by electroless metal deposition.
Schneble, Jr. et al., U.S. Pat. No. 3,226,256 and Cassat et al., U.S. Pat. Nos. 4,564,424 and 4,565,606 disclosed precatalyzed polymeric base materials containing cuprous oxide as an electroless plating catalyst for use as base materials in fully-additive printed wiring boards. Cuprous oxide is a semiconductor, and precatalyzed base materials containing cuprous oxide developed high leakage currents in use, especially when operating temperatures exceeded 50.degree. C. For this reason, the cuprous oxide precatalyzed base materials are no longer used.
Schneble, Jr. et al, U.S. Pat. Nos. 3,546,009, 3,600,330 and 3,629,185 taught insulating base materials catalytic for electroless metal deposition incorporating filler particles having a metal or metal cation of Group I-B or Group VII metals on the particles. These insulating base materials have been used in the manufacture of printed wiring boards by fully-additive processes, but they have not been accepted in the subtractive processes because the "take time" for the initiation of an electroless copper deposit was too long. Base materials are manufactured for fully-additive processes which contain a catalyst for electroless metal deposition supported on a clay filler. The FR-4 type, additive base material contains 12 parts of palladium catalyzed clay filler per hundred parts of epoxy resin.
Among the thermosetting polymers used as printed wiring base materials are phenolic, epoxy, polyimide, cyanate ester and bismaleimide triazine resins. Woven fiber reinforcements such as glass cloth, woven aramid fibers and woven quartz fibers are used in printed wiring boards.
Silane coupling agents and oganosilicon chemicals are used to upgrade the physical and electrical properties of mineral and glass filled thermoplastic resin systems to values approaching or sometimes exceeding the unfilled resin. In thermosetting resins, silane coupling agents are applied to the woven glass cloth in FR-4 laminates to improve the bond between the epoxy resin and the woven glass cloth. Silane coupling agents have also been used on alumina trihydrate in epoxy molding compounds to improve the electrical properties of the molded part. However silane coupling agents are subject to hydrolysis and are not suitable for base materials which during printed wiring board processing will be subjected to prolonged exposure to alkaline solutions.
Titanate and zirconate coupling agents react with an inorganic filler to make it hydrophobic, organophilic and organofunctional. In thermoplastic systems, filled polymers containing titanate and zirconate treated fillers have lower melt viscosity and are more easily processed than filled polymers without coupling agents. In thermosetting epoxy moldings filled with milled aramid, moldings treated with titanate coupling agents had triple the flexural and impact strength compared to moldings without coupling agents. Likewise, epoxy systems filled with potassium titanate whiskers had improved impact strength when titanate coupling agents were used. However the use of organotitanate and organozirconate coupling agents has not gained acceptance in printed wiring board base materials.